Effect of Precipitate Characteristics on the Corrosion Behavior of a AZ80 Magnesium Alloy

In this study, a systematic investigation on the effect of both aging temperature (250 °C and 330 °C) and time (chosen based on aging curves) on the distribution and volume fraction of the Mg 17 Al 12 precipitates and subsequently on the corrosion behavior of the AZ80 magnesium alloy was carried out by conducting both immersion and dynamic polarization test in a freely aerated 3.5% NaCl solution. The analysis of corrosion products using Raman spectroscopy and X-ray diffraction and investigation of corrosion morphologies using scanning electron microscopy suggested galvanic corrosion of the anodic α-Mg matrix in contact with the cathodic Mg 17 Al 12 precipitates. The higher corrosion resistance of the alloy aged at lower temperature (250 °C) was attributed to the higher number density of the Mg 17 Al 12 precipitates than that at higher temperature (330 °C). In the peak aged condition, the average number densities of precipitates (1/µm 2 ) were measured to be ~ 0.74 and ~ 0.32 and average corrosion rates (mm/y) were measured to be ~ 3.0 and ~ 5.0 at the aging temperatures of 250 °C and 330 °C, respectively. At a particular aging temperature, the corrosion resistance increased to a maximum at peak-aged condition followed by a decline in the over-aged condition and further increase with prolong aging, which was correlated with the number density, size and distribution of the Mg 17 Al 12 precipitates. Graphic Abstract